JR recently sent a comment on my claim that the word perdure is pronounced almost the same as perjure. Here is what he said:
“I have difficulty understanding the correct way to pronounce some words, e.g. that your word perdure is pronounced with a [j] sound in it. At other websites the pronunciation is given with a [d] sound in the word. Which is correct?”
In US English the SOUNDS [dy] and [ty] regularly become [j] and [ch], respectively. That is why picture is pronounced [pikchur] and verdure is pronounce [vurjur] unless they head an accented syllable. It follows that perdure would be pronounced [perjur] by speakers from the US. It is very difficult to pronounce [dyur] that way without slipping into [j].
If these sounds begin an accented syllable, this shift usually does not take place, hence most speakers would keep the [d] sound in dew, duty, and due—unless they drop the [y] in their dialects, i.e. where dew and do are pronounced the same. However, there is a little softening of the [d] even under accent.
This process is called “palatalization” because in pronouncing [d] and [t] (identical sounds except the vocal cords vibrate in pronouncing [d] ), the tongue moves to the center of the mouth, to the palate.
The same thing happens to [g] and [k] in other languages. These sounds move forward to the palate from the back of the mouth. That is why GI and CI are pronounced [j] and [ch] in Italian, e.g. Giovanni, Giuseppe, Luigi and Puccini, fettuccine.